The Supreme Court could go a number of ways on the Defense of Marriage Act repeal. Ian Millhiser counts the ways over at Think Progress:
Marriage Equality For All: The simplest, and most obvious solution, is for the justices to just follow the Constitution. The Constitution guarantees “the equal protection of the laws” to all people within the United States, and this guarantee is most robust when applied to groups that have experienced a “‘history of purposeful unequal treatment’ or been subjected to unique disabilities on the basis of stereotyped characteristics not truly indicative of their abilities.” As LGBT Americans are undoubtedly such a group, the Court should simply strike down all marriage discrimination laws and declare that every state must come into compliance with the Constitution.
Hit the link above to see the other, less desirable versions.